PTK6 and breast cancer: Expression of an alternatively spliced ALT-PTK6 transcript that lacks exon 2 and encodes a shorter 15 kDa protein containing the SH3 domain and a unique proline rich carboxy terminus, as well as transcripts encoding the full length PTK6 was previously reported in the T-47D breast cancer cell line [29] and multiple human prostate and colon cell lines [30].